1. Field of the Invention
This invention relates to a platinum catalyst and more particularly to a platinum catalyst supported on heat treated carbon particles.
2. Description of the Prior Art
Platinum is a well-known catalyst used in electrochemical cells. Electrode performance in a cell is directly related to the amount of surface area of platinum which can be reached by the various reacting species within the cell. This fact, coupled with the high cost of platinum, has resulted in considerable effort to get platinum into a usable form which has maximum surface area per unit weight of platinum. The basic approach has been, and still is, to put the platinum on the surface of suitable particles called supports. Carbon particles and graphite particles are common platinum supports in the fuel cell art. Several well-known techniques exist for depositing platinum on such supports. For example, the support can be dispersed in an aqueous solution of chloroplatinic acid, dried, and exposed to hydrogen.
By the foregoing technique, and by other techniques, platinum crystals may be uniformly distributed and highly dispersed on the surfaces of the support particles so as to provide a very high surface area of platinum.
When this supported platinum is used at temperatures greater than 100.degree.C in the presence of a liquid (or at higher temperatures in the presence of a gas) it has been found to lose surface area. This loss of surface area is particularly pronounced in an acid fuel cell environment, such as in fuel cells using phosphoric acid as the electrolyte, which operate at temperatures anywhere from 120.degree.C and higher. The loss in surface area is dramatic during the first few hours of cell operation, but it continues at a slow but steady rate for a considerable period thereafter. A loss in cell performance is directly attributable to this loss in platinum surface area.